基于滑移网格研究双流道泵内非定常流动特性

为研究双流道泵内由叶轮/蜗壳相互作用引起的非定常流动特性,基于滑移网格和RNG湍流模型计算双流道泵内的非定常流动。计算结果表明：在一个周期内,随叶轮流道相对于隔舌位置不同,其内相对速度、静压及总压分布呈周期性变化;当叶轮流道靠近蜗壳出口侧时,相对速度、静压及总压分布规律性较强;喉部为蜗壳内循环流体与叶轮排出流体的混合区域,流动最为复杂;蜗壳内各监测点的静压呈周期性变化,远离蜗壳出口的监测点的静压脉动明显大于靠近蜗壳出口的监测点的静压脉动,且越靠近喉部的监测点的静压变化越大,非定常流动特性越强烈;与定常计算相比,非定常计算所得有效扬程更符合实际情况,大于实测扬程且相对偏差仅为10%。     

不同叶轮外径下双流道污水泵压力脉动特性分析

叶轮外径是双流道污水泵的一个重要结构参数。基于Mixture多相流模型对双流道泵进行了非定常数值计算,研究了设计工况下不同叶轮外径(101、103和105 mm)对泵内压力脉动的影响,并进行了试验验证。结果表明不同叶轮外径时加入适量颗粒后蜗壳周向各点压力脉动基本均在减小且最大减幅达30.9%,各点平均压力脉动减小量随外径增大而减少。加入适量颗粒后随叶轮外径的增大隔舌附近各点压力脉动随时间的周期性越来越不明显,各点压力脉动主频基本都是叶频;随外径变大压力脉动最大幅值相比清水的减小量先增大后减小,各点平均幅值最大减小了22.7%。加入颗粒后叶轮外径增大到105 mm时动静干涉增强各点瞬时静压均剧烈波动,输送固液两相流时选择合适的叶轮外径能减小泵内压力脉动。     

颗粒参数对螺旋离心泵流场及过流部件磨损特性的影响

为了研究颗粒参数与螺旋离心泵过流部件表面磨损特性的影响,该文结合数值计算与试验方法,分别引入Mclaury和OKA 2种磨损预测模型对螺旋离心泵内固液两相流场进行求解,并将2种模型中所包含的关联因子函数进行了推导和分析,建立了颗粒参数与过流部件表面磨损的内在关联。结果表明:所采用的数值计算模型准确性较好,相对误差在可接受范围内;叶片工作面的磨损主要集中在叶片头部和螺旋段轮缘附近,叶片背面磨损主要发生在叶轮离心段,蜗壳内壁主要磨损区域为隔舌和靠近出口断面附近;颗粒粒径在0.05~0.16 mm范围内,粒径的增加促进磨损,而当粒径大于0.16 mm后,磨损增长放缓;颗粒体积分数在3%~6%范围内,颗粒体积分数的增加会加剧磨损,而从6%增加到7%时,隔舌处磨损持续增加,在周向角度为101°~326°的截面范围内,颗粒体积分数的增加会抑制蜗壳内壁磨损;颗粒速度与磨损呈正相关,且对磨损的影响较大,不同速度下蜗壳内壁各部位的磨损率变化趋势相近。在此基础上,给出了固液两相流泵水力设计和结构设计的优化方向,该文为提高两相流泵抗磨损性能提供了参考。     

结构化流道环境下不同颗粒浓度的磨粒群分布及其动力学特性

结构化表面流道内,由于流体相的驱动作用,磨粒与磨粒之间、磨粒与壁面之间产生相互碰撞,从而壁面不断受到冲击力和摩擦力而发生磨损。该文基于液-固两相流体耦合理论,利用欧拉-欧拉多相流模型中的mixture模型和Realizablek-ε湍流模型对V型纹理半环形截面流道内液-固两相流在不同颗粒浓度下运行时的壁面湍流效应进行了数值模拟,计算了流场中湍流速度及湍动性能等参数。模拟结果表明:V型纹理的流道有利于涡流的产生,因此可以通过配置V型纹理的约束模块来提高湍流的紊乱程度;随着颗粒浓度的增大,在一定范围内磨粒流的速度逐渐增大,磨粒流的湍动能逐渐减小,磨粒体积分数的波动振幅越来越小;颗粒浓度的选择应适当,不同的颗粒浓度可以产生不同的磨粒流综合性能和颗粒分布效果。     

双流道泵叶轮内湍流的数值模拟

对双流道泵叶轮内3维不可压湍流流动进行了数值模拟。计算采用了雷诺时均N-S方程和修正了的k-ε湍流模型,计算在体贴坐标系和交错网格中进行并采用了SIMPLE-C算法。计算结果首次揭示了双流道泵叶轮内湍流流动的速度分布、压力分布和湍动能分布规律。研究结果可以用来对双流道泵进行性能预测并为双流道泵的优化设计创造了条件     

离心泵气液固多相流动数值模拟与试验

为研究离心泵输送含有气固液多相时内部的流动情况,采用Pro/E三维造型软件进行几何造型,基于ANSYSCFX软件应用雷诺时均方程、双方程湍流模型,并结合SIMPLEC算法对其内部三维气固液多相流各相流动规律进行数值计算,将计算结果与试验结果进行对比结果表明:受气相所产生旋涡的影响,固相体积分数在径向量纲位置r/R2为0.4时达到最大值后直线急剧下降,下降至一定值后开始波动变化,而气相体积分数在径向量纲位置r/R2为0.4时较小,从径向量纲位置r/R2为0.4以后急剧增大。气、固两相互相影响对方颗粒的分布。气相主要集中在叶片工作面的中间位置,气相的存在使叶轮流道内产生旋涡,影响叶轮流道内的能量交换与传递;固相在没有旋涡的流道内是紧靠叶片表面运动的,在有旋涡流道内主要是随着旋涡旋转方向进行流动,固相所占比值的增加对流动轨迹的影响并不明显。对气液固多相流的深入研究和应用提供了有价值的参考。     

双流道泵水力设计的研究

在大量试验研究和设计实践的基础上，对双流道泵叶轮和蜗壳的一些主要几何参数进行了统计分析，发展和完善了双流道泵水力设计方法。给出了双流道泵叶轮轴面图前、后盖板圆弧半径R₁、R₂与比转数n_s及叶轮进、出口直径D_j、D₂的关系，提出了叶轮平面图流道中线方程。总结了双流道泵蜗壳基园直径D₃、进口宽度b₃、隔舌角φ₀和面积比系数y的计算公式。     

后掠式叶片轴流泵固液两相流数值模拟与优化

针对轴流叶轮在污水固液两相流介质中的磨损问题,该文设计了不同后掠式叶轮结构方案进行优化设计,分别对后掠角度为40°、65°、90°的后掠叶片和原型叶片进行固液两相流数值模拟和试验对比,并分析了不同后掠方案叶轮内固体颗粒的分布特性。数值模拟结果表明,随着后掠角度的增加,叶片压力面固相体积分数会逐渐减少,而叶片吸力面上固相体积分数会先增加后减小,叶轮内固相的径向流动越明显并且叶片后掠角度越大,固相就越难与叶片压力面接触,而越易与叶片吸力面接触;颗粒直径越大,后掠叶片压力面上固相体积分数越大,而叶片吸力面进口边靠近轮毂处的固相体积分数增加;颗粒浓度越大,后掠叶片压力面上固相体积分数减少,叶片吸力面上固相体积分数增加。当优化后的后掠叶片角为90°时,该叶片结构优化了固体颗粒的分布,可大幅降低叶片轮缘处的磨损,提高了轴流叶轮在污水介质中的使用寿命和运行可靠性。     

双流道泵性能预测的研究

通过对双流道泵叶轮和蜗壳里的水力损失、容积损失、机械损失的分析，提出了双流道泵扬程曲线、效率曲线的性能预测方法。分别给出了双流道泵叶轮和蜗壳内各种摩擦损失、扩散损失，及主要局部损失的计算方法。性能预测实例表明预测结果具有较高的精度。     

泵内大颗粒固液两相流流动试验

为了研究泵内大粒径球形颗粒运动规律,该研究以一台单级单吸悬臂式离心泵作为研究对象,采用高速摄影试验测试的方法对大粒径球形颗粒在固液两相流泵内的运动轨迹、通过性能以及颗粒与隔舌的碰撞规律进行了研究。测试结果表明:不同粒径的球形颗粒在泵内的轨迹变化规律相似,在叶轮进口处均有向叶片背面运动的趋势,而在运动过程中又逐渐脱离叶片背面,向下一叶片工作面靠近;泵内不同粒径颗粒运动趋势基本相同,但相对运动轨迹长度有所改变;粒径为8 mm和10 mm时颗粒平均过泵时间相对于粒径为6 mm时分别下降了15.15%和11.03%。颗粒体积分数对泵内对颗粒运动轨迹的影响较小,不同体积分数下泵内颗粒的运动轨迹基本重合;体积分数为3%和5%时颗粒平均过泵时间相比体积分数1%时分别上升了4.38%和3.21%。颗粒体积分数为1%、3%和5%时,颗粒与隔舌的碰撞的概率分别为0.5%,0.69%和0.9%;颗粒粒径为6 mm,8 mm和10 mm时颗粒与隔舌发生碰撞的概率分别为0.69%,0.63%和0.55%。研究结果可为运输大颗粒两相流泵的结构设计和防磨损研究提供参考。     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.